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  1. #1
    psi
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    Getting more speed out of a folding bike with 16" wheels (SRAM Automatix?)

    Someone gave me a folding bike with 14" wheels, a "Roll n Fold" (cheap department store folding bike.) I was finding the gearing way too low for the wheel size (something like 32x18), so I swapped the rear wheel for a 16x1.75" coaster brake wheel from a kid's bike that uses the same type of cogs as a 3-speed. The new configuration is 42x13 which gives 3.5 meters development or 43.5 gear inches. (I also switched the front to a 16" wheel too by using forks from a kids' suspension MTB.) I may swap the 42t for something bigger at some point too. As it is now it's much more fun to ride than with the stock setup.

    What I would like to do is build a rear wheel the same size around something like an Automatix 2-speed. I'm figuring the extra overdrive gear would give 4.7m or 59.2 gear inches. The thing is, I'm not coming up with much in my online searches for 16" rims with 36 spoke holes and I don't know a lot about selecting rims generally. I weigh 160 lbs and I'm basically looking for something fairly inexpensive that's strong enough to make a durable wheel. I'm thinking that with so many spokes on such a small wheel the rim may not need to be anything too fancy, but as I say I don't really know a lot about this stuff. I have done some reading on wheelbuilding but haven't done it.

  2. #2
    coprolite fietsbob's Avatar
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    Consider skipping holes in the hub, and only using enough to suit your rim drilling..

    so a 28 spoke rim , skip 4 holes on each hub-flange side.
    Last edited by fietsbob; 09-24-12 at 05:34 PM.

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    I am working on a Scooma folding bike and have struggled with the same problem. I was looking for a freehub to fit a cassette. Most of the 16" rims off of kids bike have 28h drillings and 28h freehubs are not too common.

    You may want to consider a 3 speed sturmey archer hub. With the right sized cog, they do provide decent gearing.

    Otherwise, I do believe Sunrims make a 32h 16" rim.

  4. #4
    psi
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    Quote Originally Posted by fietsbob View Post
    Consider skipping holes in the hub, and only using enough to suit your rim drilling..

    so a 28 spoke rim , skip 4 holes on each hub-flange side.
    I've seen some mention of that practice online. Is there any functional downside?

    Also special_k I checked out those 16" sun rims and the price sounds good, a little over $30 at the first place I looked.
    Last edited by psi; 09-24-12 at 06:05 PM.

  5. #5
    Member ryukenden's Avatar
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    I'm curious to see how this goes. some upgrade could cost more than the bike. Why not get a decent used foldie and mod that?
    Current: 2012 Tern Link D8 w/Brooks B17

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    16" 36h rims here

    http://www.sjscycles.co.uk/sun-cr18-...hole-prod8542/

    It is also possible to get Automatix hubs with 28h from Germany.

    http://www.ebay.de/sch/i.html?_sacat...ix+sram&_frs=1

    Again with or without coaster brake.

    I have a non coaster 28h version fitted on my Brompton. I did have to work on the OLN to narrow it down to slimmer 117mm Brompton rear fork spacing.




    Jerry
    Last edited by jerrysimon; 09-28-12 at 01:54 PM.

  7. #7
    psi
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    Looks good jerrysimon, I think I came across your thread on that bike on google when reading up on the Automatix a little while ago. Sounds like fun to ride. I'd like to try a 50t+ gear in the front sometime but that would require a new crankset.

    I'm thinking the 36h route probably makes more sense for me as it looks pricier to get those 28h ones from germany. (I'm in Canada). The cheapest I've been able to find so far is about $50 from Amazon for the non-coaster, 36 hole model.


    Quote Originally Posted by ryukenden View Post
    I'm curious to see how this goes. some upgrade could cost more than the bike. Why not get a decent used foldie and mod that?
    I usually only buy something new for a low value bike if it's likely to be usable on other/better bikes later if desired, so I would be putting money into this wheel with that in mind. Also, I have grown to like this bike in spite of the initial shortcomings. I do have a shimano 3-speed hub that could be used for something like this, but an automatic transmission on a bike sounds fun.

  8. #8
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    I have a 60t front, 12t rear, 175 cranks, and 305 rims.
    The Sheldon calculator puts me at 67.3 gear inches which is a great single speed/cruising setup.
    Perhaps if you get a huge chainring (if it fits) things will be better.

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    coprolite fietsbob's Avatar
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    I'm finding it a bit harder to get the pump on the stem on a 20" 32 spoke
    the 28 hole 349 16" is OK, but 36 hole 305 will be rather dense..
    like hard stunt rider BMX 406 48 spoke..

    Note there is a 24 hole 349 rim, bike friday Tikit uses lots of them ..

    and there are 100psi tires for those rims, for the need for speed..

  10. #10
    tcs
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    Quote Originally Posted by psi View Post
    I do have a shimano 3-speed hub that could be used for something like this, but an automatic transmission on a bike sounds fun.
    With the same chainwheel and cog, the top gear ratio using a Shimano (or SRAM or Sturmey-Archer) 3-speed hub will be lower than the top gear ratio using a SRAM Automatix (or Sturmey-Archer Duomatic). You'd gain another, lower gear, of course.
    "When man first set woman on two wheels with a pair of pedals, did he know, I wonder, that he had rent the veil of the harem in twain? A woman on a bicycle has all the world before her where to choose; she can go where she will, no man hindering." The Typewriter Girl, 1899.

    "Every so often a bird gets up and flies some place it's drawn to. I don't suppose it could tell you why, but it does it anyway." Ian Hibell, 1934-2008

  11. #11
    coprolite fietsbob's Avatar
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    S3X the fixie 3 speed is the lower 3/5ths of the 5 speed, ratio-wise.

    The AW3 is the direct gear in the middle of 1)3/4 & 3)4/3, (.75, 1.33 )
    which are also the middle 3 on the current 5 speed .. (1, is .63, 5 is 1.6 )

    so to get a taller High-gear consider the actual 5 speed ..

  12. #12
    psi
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    Quote Originally Posted by tcs View Post
    With the same chainwheel and cog, the top gear ratio using a Shimano (or SRAM or Sturmey-Archer) 3-speed hub will be lower than the top gear ratio using a SRAM Automatix (or Sturmey-Archer Duomatic). You'd gain another, lower gear, of course.
    That's a good point, the extra overdrive is a nice feature. I have a 20" sachs 3-speed wheel with the same higher overdrive ratio (I guess SRAM is essentially the same company with a different name.) Unfortunately there is no control chain on it so I can only use it as a 1-speed. I used to have another 20" folding bike with a Sachs kickback 2-speed, but unfortunately I lost the keys and later the entire rack it was locked to disappeared when they did some construction nearby.

    I also had another project in mind for the shimano 3-speed, a Gitane road bike that has a 26" 3-speed wheel currently but should have a 27" wheel.

    For reference, here's what the bike I was originally talking about looks like:

    roll n fold.jpg

  13. #13
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    Interesting bike. At least the saddle and bar height make it a more comfortable looking ride ?

    Also nice to see suspension on the front with those smaller wheels. I think I might want some on the rear as well though.

    What is the rear frame spacing as this may limit the available choice of rear hubs ?

    Regards

    Jerry

  14. #14
    psi
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    I'll check the spacing later today, thinking I will pull the trigger on a non-coaster Automatix 36h if the spacing looks like it will work. I generally find the geometry pretty comfortable on level ground, but I may switch the stem/handlebars eventually as it's hard to lean forward much to climb. I've tried a suspension seatpost on the bike but unfortunately the one I have is too short for my height. The seatpost diameter is larger than whatever the most common size is.

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    If its like the Brompton and narrower than 120mm OLD, you may have to remove one of the lock nuts and or/machine the thickness of one down.

    It can be used on bikes with 130mm OLD as well, using the two supplied 5mm spacers.

    Regards

    Jerry
    Last edited by jerrysimon; 09-27-12 at 11:40 AM.

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    Senior Member SJX426's Avatar
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    Have you considered a Capreo hub and cassette?
    http://sheldonbrown.com/capreo/index.html

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    Quote Originally Posted by SJX426 View Post
    Have you considered a Capreo hub and cassette?
    http://sheldonbrown.com/capreo/index.html
    Interesting option to reduce the OLN down to 123mm assuming the locking nut would still be needed.

    Although I can see how removing the spacers would reduce the OLN, would you then need to cut the axle down and shorten the quick release pin ?

    Ah just read it

    "By removing spacers and trimming the axle, this hub could easily be adapted to other spacings, though this would result in a wheel with more dish."

    Regards

    Jerry
    Last edited by jerrysimon; 09-28-12 at 01:55 PM.

  18. #18
    psi
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    The Capreo system sounds interesting, I was not aware that 9t sprockets were something you could get.


    The distance between the dropouts is something like 115 mm. Sounds like it's possible to work something out with the automatix. Jerry, could you expand a little on something you were saying in the other thread?

    The hub is specified for a 16T sprocket minimum which just fits in the frame without fouling the end of the chain stay. I guess you could use smaller sprockets but when I tried one you can't then get the dust cover on and the chain line is all wrong.
    If I can't use a smaller cog than a 16 then that limits things a lot without a bigger gear in front. I'm thinking I will buy the hub though regardless, worst case I can just use it for a 20" wheel for another bike.

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    Re size of rear sprocket it all depends on your chain line. On the Brompton you have to use a dished sprocket to get the chain line right so that restricts you to the 16T being the smallest dished sprocket you can get. If your chain line is ok you may be able to use a smaller toothed non dished one though I doubt you will be able to fit the dust cover.

    Re the OLN of the Automatix its 120mm without the spacers. The two lock nuts on the non drive side are about 2.5mm each if I recall. The Brompton rear dropout width spacing is around 117mm so I needed to loose about 3mm. I removed one of the lock nuts and then had the other one machined down to about 1.5mm - 2mm and just used that. It means you have to "set" the nut to lock the hub together when you clamp it between the dropouts. You should be ok doing the same, though maybe have to spread your forks very slightly.

    Note also on 14" wheels you will almost certainly have to change the gear change speed which will be set for much larger wheels and will probably change on your 14" wheels at some ridiculously low speed. Details of how to do this are linked in one of the TSR2 Automatix conversion threads.

    The S/A S2C (two speed manual kick back to change gear) has a smaller 116mm OLN. I tried two of these when they first came out but don't rate them over the smooth operation of the SRAM Automatix.

    Regards

    Jerry
    Last edited by jerrysimon; 09-28-12 at 02:01 PM.

  20. #20
    coprolite fietsbob's Avatar
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    Looking at the picture , question the economics of .. a pig's ear,
    no matter how many earrings you hang on it , it's still a pig's ear,
    attached to what it is.. not a silk purse..

    now you decided you want a more efficient rolling bike .. Shop for one of those..

  21. #21
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    I actually quite like this bikes quirky appeal/look

    Not sure how good the frame geometry is but it looks like a nice high (legs straight at bottom pedal position) ride. If you have the parts IMHO its worth some playing around with.

    How many teeth has the main chain ring got ?

    That might be a challenge to get a high enough gear given the small wheels, even if you use a smaller sprocket.

    Jerry

  22. #22
    coprolite fietsbob's Avatar
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    looks like about a 46.. the OP could buy one of brompton's 54t crankests
    Or another crank with a removable chain ring , and substitute one of the 60t
    for what it came with..
    [work backwards you will find few 60t rings is lots of bolt patterns.
    but you can find a number of choices of crankset with the Bolt diameter circle known
    for the replacement chainring.

  23. #23
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    Yes I have used Brompton cranksets on other bikes before. Next years Brompton updated parts promise a new Brompton crankset with removable rings

    Regards

    Jerry

  24. #24
    psi
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    Checking again it is a 46, I think I said 42 earlier.

    Mostly the project is an excuse to give one of those hubs a try. I think ultimately it does make sense to get a crank with a removable chain ring to up the gearing, but I will probably hold off until later to do that.

    A funny thing about this bike is that the original forks were just straight; the front axle was directly in line with the steering axis instead of offset like on any normal bike. The steering was weird to say the least.

  25. #25
    psi
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    I put in the order for the hub, which worked out to be about $75 shipped to Canada. Still not decided on whether it makes more sense to use the hub on a 16" wheel for that silver bike or a 20" one for another folding bike. I'm leaning towards the 20" because I already have a rim I could use for that, and I'd get more out of the gearing on a bigger wheel.

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